This invention generally relates to thermoplastics and articles formed therefrom. More particularly, the invention relates to macrocyclic polyester oligomer compositions and methods for modifying physical and chemical properties of the compositions. Even more particularly, this invention relates to macrocyclic-polyester oligomer compositions having relatively low melting temperatures.
Linear polyesters such as poly(alkylene terephthalate) are generally known and commercially available where the alkylene typically has 2 to 8 carbon atoms. Linear polyesters have many valuable characteristics including strength, toughness, high gloss and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a dicarboxylic acid or its functional derivative, typically a diacid halide or ester. Linear polyesters may be fabricated into articles of manufacture by a number of known techniques including extrusion, compression molding, and injection molding. Linear polyesters may be produced from macrocyclic polyester oligomers.
Macrocyclic polyester oligomers (MPOs) have unique properties that make them attractive as matrices for engineering thermoplastic composites. These desirable properties stem from the fact that MPOs exhibit low melt viscosity, allowing them to impregnate a dense fibrous preform easily. Furthermore, certain MPOs melt and polymerize at temperatures well below the melting point of the resulting polymer. Upon melting and in the presence of an appropriate catalyst, polymerization and crystallization can occur virtually isothermally. As a result, the time and expense required to thermally cycle a tool is favorably reduced.
Generally speaking, MPO compositions have high melting temperatures, which necessitate the use of special equipment in processing not commonly available in polymer processing units. If compositions with lower melting temperatures could be produced, it would be possible to use more readily available processing equipment such as that is commonly used in the production and handling of epoxy resins.
Physical and/or chemical properties of MPO compositions may be significantly modified by modifying the weight percentage of one or more of the constituent MPOs. For example, the presence of a single MPO species, the macrocyclic polyester tetramer, has an unexpectedly pronounced effect on the melting temperature of MPO composition. Removal of a portion of the macrocyclic polyester tetramer can result in low-melting MPO compositions. The resulting MPO compositions have the further advantage, under many circumstances, of a greatly reduced tendency to crystallize at ambient temperatures, making it possible to combine them with fillers such as carbon or glass fibers to produce prepregs easily convertible to filled high molecular weight linear polyesters.
In one aspect, the invention is related to a process for modifying a physical property of a composition that includes MPOs. The process includes the steps of (a) providing a composition that has at least two species of MPOs, and (b) changing the weight percentage of at least one species of the MPOs in the composition.
In another aspect, the invention is related to a MPO composition that includes at least two species of MPOs wherein a species of the MPOs having the highest melting temperature is present in an amount less than or equal to 5%. In one embodiment, a blend material includes such a MPO composition and also a polymerization catalyst.
In a preferred embodiment, a MPO composition of the invention comprises 30-40% macrocyclic polyester dimers, 30-45% macrocyclic polyester trimers, 0-5% macrocyclic polyester tetramers, and 5-20% macrocyclic polyester pentamers.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following figures, description, and claims.